Spread-spectrum communications utilizing variable throughput reduction

ABSTRACT

A spread-spectrum system having a transmitted data rate determined by an error rate syndrome at a spread-spectrum receiver. Data are demultiplexed into a plurality of data channels, and spread-spectrum processed as a plurality of spread-spectrum channels. A combiner combines the plurality of spread-spectrum channels as a code-division-multiplexed signal. At a receiver, the code-division-multiplexed signal is despread into a plurality of despread channels. A multiplicity of adders, which is electronically controlled by an adder-control signal, adds several of the despread channels to generate a multiplicity of added channels. A syndrome signal is generated from an error rate of the multiplicity of added channels. From the syndrome signal, a desired-data rate is determined for the spread-spectrum transmitter.

RELATED PATENTS

This patent stems from a continuation application of U.S. patentapplication Ser. No. 09/946,841, and filing date of Sep. 6, 2001,entitled VARIABLE THROUGHPUT REDUCTION SPREAD-SPECTRUM COMMUNICATIONS byinventor, JOSEPH GARODNICK, which stems from a continuation applicationof U.S. patent application Ser. No. 09/594,440, and filing date of Jun.14, 2000, entitled SPREAD-SPECTRUM COMMUNICATIONS UTILIZING VARIABLETHROUGHPUT REDUCTION by inventor, JOSEPH GARODNICK, which issued on Sep.11, 2001, as U.S. Pat. No. 6,289,039. The benefit of the earlier filingdate of the parent patent application is claimed for common subjectmatter pursuant to 35 U.S.C. § 120.

BACKGROUND OF THE INVENTION

This invention relates to spread-spectrum communications, and moreparticularly to spread-spectrum communications using parallel channels,preferably employing orthogonal chip-sequence signals, with error rateand data rate feedback.

DESCRIPTION OF THE RELEVANT ART

In a packet-communications spread-spectrum multi-cell system, high-speeddata can be implemented with the prior art method of parallel channels,using parallel chip-sequence signals. By using multiple correlators ormatched filters, multiple-orthogonal chip-sequence signals can be sentsimultaneously thereby increasing the data rate while still enjoying theadvantage of a high processing gain. The multiple chip-sequence signalsbehave as multiple users in a single location. Multipath is amelioratedby a RAKE receiver, and the interference to be overcome by theprocessing gain is that generated by other users, in the same oradjacent cells. When such interference occurs, it is called a collision.

Normally, when a remote station is within a cell or cell sector, asillustrated in FIG. 1, the path differences from base stations locatedin the adjacent cells ensure that the interference is small enough so asnot to cause the error rate of the wanted signal to deteriorate below ausable level. When the remote station is near the edge of the cell,however, the interference can be substantial as the interference canresult from two adjacent cells.

One method that has been used to overcome this problem in a conventionalspread-spectrum system is to increase the processing gain in order toincrease the immunity from interference. To do this, in a fixedbandwidth system, the data rate is reduced, and the integration time ofthe correlator or the length of the matched filter is increasedaccordingly. This method, however, changes the length of the correlatorsequence, or changes the size of the matched filter; both of whichimpact the architecture of the receiver. In addition, with increasedintegration times, the chip-tracking loop and phase-tracking loop haveto function flawlessly and the allowable frequency offset must bereduced, requiring at least a frequency locked loop.

Another method in the prior art is to repeat the symbols sequentiallyand add the result of the individually received symbols. This methodchanges the timing of the receiver and the framing of the data at thetransmitter.

SUMMARY OF THE INVENTION

A general object of the invention is to vary the throughput of atransmitted spread-spectrum signal.

Another object of the invention is to set the throughput of atransmitted spread-spectrum signal based on a required error rate at aspread-spectrum receiver.

An additional object of the invention is to control a data rate of aspread-spectrum transmitter from a spread-spectrum receiver, using aclosed loop method.

According to the present invention, as embodied and broadly describedherein, a spread-spectrum system is provided comprising, at aspread-spectrum transmitter, a demultiplexer, a plurality offorward-error-correction (FEC) encoders and interleavers, a plurality ofspread-spectrum processors, a combiner, and a modulator. At aspread-spectrum receiver, the system comprises a demodulator, aplurality of spread-spectrum despreaders, a multiplicity of adders, amultiplicity of FEC decoders and de-interleavers, a command processor,and a multiplexer.

The demultiplexer demultiplexes input data into a plurality of datachannels. The plurality of forward-error-correction encoders andinterleavers FEC encodes and interleaves the plurality of data channels,as a plurality of FEC encoded and interleaved channels, respectively.

The plurality of spread-spectrum processors spread-spectrum processesthe plurality of FEC encoded and interleaved channels as a plurality ofspread-spectrum channels. The plurality of spread-spectrum channels usesa plurality of chip-sequence signals to define a particularspread-spectrum channel. Preferably, the plurality of chip-sequencesignals is a plurality of orthogonal chip-sequence signals, however, aplurality of quasi-orthogonal chip-sequence signals may be used.

The combiner combines the plurality of spread-spectrum channels as acode-division-multiplexed signal. The modulator transmits thecode-division-multiplexed signal with the plurality of spread-spectrumchannels, over a communications channel.

At the receiver, the demodulator translates thecode-division-multiplexed signal to a processing frequency, and theplurality of spread-spectrum despreaders despreads thecode-division-multiplexed signal into a plurality of despread channels,respectively.

The multiplicity of adders is electronically controlled by anadder-control signal. The multiplicity of adders adds at least twodespread channels to generate a multiplicity of added channels.

The multiplicity of FEC decoder and de-interleavers generates a syndromesignal from an error rate of the multiplicity of added channels. Themultiplicity of FEC decoders and de-interleavers, FEC decodes andde-interleaves the multiplicity of added channels, as a multiplicity ofdecoded channels.

In response to the syndrome signal, the command processor determines adesired-data rate, and generates a data-rate command signal having thedesired data rate for the spread-spectrum transmitter. The commandprocessor also generates the adder-control signal for adding together anumber of despread channels of the plurality of despread channels, andgenerates a multiplexer signal having a number of decoded channels tomultiplex together. The multiplexer multiplexes the multiplicity ofdecoded channels to generate an estimate of the input data.

The data-rate command signal is sent to the spread-spectrum transmitter.The data-rate command signal controls into how many data channels thedemultiplexer demultiplexes the input data. Assume the demultiplexer, byway of example, demultiplexes input data into 16 parallel channels. Ifthe processor in the receiver determines, as a response to the syndrome,that the input data are to be sent at twice the power of a single datachannel of the plurality of data channels, then pairs of data channelsin the plurality of data channels have identical data, with a resultingeight sets of data having different data per set. Each set of datacomprises two data channels with identical data.

Additional objects and advantages of the invention are set forth in partin the description which follows, and in part are obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention also may be realized and attained bymeans of the instrumentalities and combinations particularly pointed outin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate preferred embodiments of theinvention, and together with the description serve to explain theprinciples of the invention.

FIG. 1 illustrates a cellular architecture depicting a problem area froma remote station near a boundary;

FIG. 2 is a block diagram of a spread-spectrum transmitter usingparallel channels;

FIG. 3 is a block diagram of a spread-spectrum receiver for receivingparallel channels;

FIG. 4 is a block diagram of a spread-spectrum transmitter having a databuffer, and a demultiplexer controlled by a data-rate command signal,and using parallel channels;

FIG. 5 is a block diagram of a spread-spectrum receiver for receivingparallel channels, with an error rate and a data rate command processor;

FIG. 6 is a block diagram of a spread-spectrum receiver for receivingparallel channels, using matched filter or SAW technology, with an errorrate and a data rate command processor; and

FIG. 7 is a flow chart of controlling data rate of a spread-spectrumtransmitter, based on error rate at a spread-spectrum receiver.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference now is made in detail to the present preferred embodiments ofthe invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals indicate like elementsthroughout the several views.

The present invention employs a command processor with a parallelspread-spectrum system, for determining from an error rate, adesired-data rate. In a preferred embodiment, the desired-data ratemeets an error rate criterion, such as fewer errors than a desired errorrate. The error rate is from a syndrome, generated in aforward-error-correction decoder.

A spread-spectrum signal, as used herein, typically includes a datasignal, multiplied by a chip-sequence signal, and multiplied by acarrier signal. The data signal represents a sequence of data bits. Thechip-sequence signal represents a sequence of chips, as normally used ina direct sequence, spread-spectrum signal. The carrier signal is at acarrier frequency, and raises the product of the data signal and thechip-sequence signal, to the carrier frequency.

For synchronization, the data signal typically is a constant value, forexample, a series of one bits, or some sequence known a priori, or hasvery slowly time-varying data. The spread-spectrum signal may be apacket, with a header followed by data, or a plurality ofspread-spectrum channels, with one of the spread-spectrum channels usedfor synchronization. A particular spread-spectrum channel is defined bya particular chip-sequence signal, as is well known in the art. For thecase of the packet, synchronization is performed on the header, as iswell-known in the art. For a dedicated spread-spectrum channel,synchronization is performed from the dedicated channel.

At a spread-spectrum transmitter, the spread-spectrum system includesdemultiplexer means, encoder means, spreader means, combiner means, andmodulator means. The encoder means in coupled between the demultiplexermeans and the spreader means, and the combiner means is coupled betweenthe spreader means and the modulator means. The input data enters thedemultiplexer means.

The demultiplexer means demultiplexes input data into a plurality ofdata channels. The encoder means FEC encodes and interleaves theplurality of data channels as a plurality of FEC encoded and interleavedchannels, respectively. The spreader means spread-spectrum processes theplurality of FEC encoded and interleaved channels as a plurality ofspread-spectrum channels. The plurality of spread-spectrum channels hasa plurality of chip-sequence signals, respectively. A particularchip-sequence signal defines a particular spread-spectrum channel, as iswell-known in the art.

The combiner means combines the plurality of spread-spectrum channels asa spread-spectrum signal. The modulator means transmits thespread-spectrum signal having the plurality of spread-spectrum channels,over a communications channel. A spread-spectrum signal is transmittedover a communications channel by the modulator means.

At a spread-spectrum receiver, the system includes demodulator means,despreader means, adder means, decoder means, command means, andmultiplexer means. The despreader means is coupled between thedemodulator means and the adder means. The decoder means is coupledbetween the adder means and the multiplexer means. The command means iscoupled to the adder means, decoder means and demultiplexer means. Thecommand means further provides data to a communications link to thespread-spectrum transmitter, and to the demultiplexer means.

The demodulator means translates the code-division-multiplexed signal toa processing frequency. The despreader means despreads thecode-division-multiplexed signal into a plurality of despread channels,respectively.

The adder means electronically is controlled by an adder-control signal.The adder means adds none or at least two despread channels to generatea multiplicity of added channels. The decoder means generates a syndromesignal from an error rate of the multiplicity of added channels. Thedecoder means also FEC decodes and de-interleaves the multiplicity ofadded channels, and a multiplicity of decoded channels.

In response to the syndrome signal, the command means determines adesired-data rate, and generates a data-rate command signal having thedesired data rate. The command means also generates the adder-controlsignal for controlling the adder means, for adding together a number ofdespread channels of the plurality of despread channels. The commandmeans generates a multiplexer signal for controlling the multiplexermeans. The multiplexer means has a number of decoded channels tomultiplex together.

The data-rate command signal is sent to the spread-spectrum transmitter.The data-rate command signal controls the demultiplexer means. Thedata-rate command signal determines the number of data channels intowhich input data are demultiplexed. Assume the demultiplexer means candemultiplex input data into a maximum of M data channels, where M is thenumber of data channels. If the processor means determined from thesyndrome, that twice the power were required from the transmitter tomaintain or reduce an error rate, then the data-rate command signalcontrols the multiplexer means to send the input data as two identicalsets of M/2 data channels. In general, if the processor means determinesfrom the syndrome, that N times the power is required, then thedata-rate command signal controls the multiplexer means to send theinput data as N identical sets of M/2 data channels.

The multiplexer means multiplexes the multiplicity of decoded channelsand generates an estimate of the input data.

As illustratively shown in FIG. 2, the demultiplexer means is embodiedas a demultiplexer 31, the encoder means in embodied as a plurality ofFEC encoders and interleavers 32, and the spreader means is embodied asa plurality of spreaders 33. The combiner means is embodied as acombiner 36, and the modulator means is embodied as a modulator 37. Atransmitter antenna is coupled to the modulator 37.

The demultiplexer receives input data. The plurality of FEC encoders andinterleavers 32 is coupled between the plurality of outputs from thedemultiplexer 31, and the plurality of spreaders 33. The combiner 36 iscoupled between the plurality of spreaders 33 and the modulator 37. Theplurality of spreaders 33 may include a chip-sequence generator 39 forgenerating the plurality of orthogonal chip-sequence signals or aplurality of quasi-orthogonal chip-sequence signals, and a plurality ofproduct devices 40, coupled to the chip-sequence generator 39. Theplurality of product devices 40 spread-spectrum processes the pluralityof encoded channels as the plurality of spread-spectrum channels. Theplurality of spreaders, as is well-known in the art, alternatively maybe embodied as a plurality of matched filters having a plurality ofimpulse responses matched to the plurality of chip-sequence signals, ora memory device for storing the plurality of chip-sequence signals.

The demultiplexer 31 demultiplexes input data into a plurality of datachannels. The plurality of forward-error-correction encoders andinterleavers 32, FEC encode and interleave the plurality of datachannels as a plurality of FEC encoded and interleaved channels,respectively. The plurality of spreaders 33 spread-spectrum processesthe plurality of FEC encoded and interleaved channels with as aplurality of spread-spectrum channels. The plurality of spread-spectrumchannels is defined by a plurality of chip-sequence signals, as iswell-known in the art.

The combiner 36 combines the plurality of spread-spectrum channels as acode-division-multiplexed signal, and the modulator 37 transmits,through the transmitter antenna 38, the code-division-multiplexed signalwith the plurality of spread-spectrum channels, over a communicationschannel.

In the exemplary arrangement shown in FIG. 3, the demodulator means isembodied as a demodulator 51, and the despreader means is embodied as aplurality of despreaders 52. The adder means is embodied as amultiplicity of adders 53. The decoder means is embodied as a pluralityof FEC decoders and de-interleavers 56, and the demultiplexer means isembodied as a demultiplexer 31.

The demodulator 51 is coupled to the communications channel throughantenna 48. The plurality of despreaders 52 is coupled between thedemodulator 51 and the plurality of FEC decoders and de-interleavers 56.The plurality of FEC decoders and de-interleavers 56 is coupled betweenthe multiplicity of adders 53 and the multiplexer 57.

The demodulator 51 translates the code-division-multiplexed signal to aprocessing frequency. The plurality of despreaders 52 despreads thecode-division-multiplexed signal into a plurality of despread channels,respectively. The plurality of despreaders 52 may be embodied, as iswell-known in the art, as a plurality of matched filters or a pluralityof correlators.

The multiplicity of FEC decoder and de-interleavers 56 generates asyndrome signal from an error rate of the multiplicity of addedchannels, and FEC decodes and de-interleaves the multiplicity of addedchannels, as a multiplicity of decoded channels. The multiplexer 57multiplexes the multiplicity of decoded channels and generates anestimate of the input data.

The prior art spread-spectrum transmitter and receiver, as shown inFIGS. 2 and 3, use parallel chip-sequence signals. The data to betransmitted are first de-multiplexed by a demultiplexer 31 to produce aplurality of uncorrelated data channels. Each uncorrelated data channelhas at a lower data rate than the original data rate of data enteringthe demultiplexer 31. For example, if the incoming data rate were 16megabits per second (Mbps), and the incoming data were de-multiplexed to16 data channels, with each data channel at one Mbps.

The plurality of data channels is forward error correction (FEC) encodedand interleaved by a plurality of FEC encoders and interleavers 32,respectively, to generate a plurality of FEC encoded and interleaveddata channels. FEC encoders and interleavers are well-known to theordinary skilled artisan, and found in many technical journal articlesand textbooks.

A plurality of spreaders 33 spread-spectrum processes the plurality ofFEC encoded and interleaved data channels, as a plurality ofspread-spectrum channels. A spreader typically is a product device formultiplying a data-sequence signal by a chip-sequence signal. Ade-spreader equivalently may be realized from a matched filer or SAWdevice, as is well-known in that art.

In FIG. 2, the plurality of spreaders 33 includes a chip-sequencegenerator 34 for generating a plurality of chip-sequence signals and aplurality of product devices 35. In a preferred embodiment, theplurality of chip-sequence signals is a plurality of orthogonalchip-sequence signals, although a plurality of quasi-orthogonalchip-signal sequence signals also could be used. By quasi-orthogonalchip-sequence signals is meant chip-sequence signals which are nearlyorthogonal or which are not orthogonal but have orthogonal typequalities.

The plurality of product devices 35 is coupled to the chip-sequencegenerator 34, and to the plurality of encoders and interleavers 32,respectively. The plurality of product devices 35 spread-spectrumprocesses the plurality of FEC encoded and interleaved data channels, asa plurality of spread-spectrum channels. A product device my be embodiedas an AND gate, or equivalently from one or more combinations of ANDgates, NAND gates, NOR gates, gates or EXCLUSIVE-OR (XOR) gates. Analternative for the plurality of spreaders 33 is a plurality of matchedfilters or a plurality of surface acoustic wave devices, each having animpulse response matched to one of the chip-sequence signals in theplurality of chip-sequence signals.

The outputs of the plurality of spreaders 33 are combined by a combiner36 and sent to the modulator 37 and transmitted over a communicationschannel. The combiner 36 preferably linearly combines the plurality ofspread-spectrum channels, as a code-division-multiplexed signal having amultiplicity of channels. The combiner 36 alternatively may non-linearlycombine the plurality of spread-spectrum channels, in some applications.The multiplicity of channels is defined by a respective chip-sequencesignal, used for a spread-spectrum channel in the plurality ofspread-spectrum channels, as is well-known in the art. The spreaders canoperate at a chip rate depending on the desired processing gain.

In the spread-spectrum receiver, the process is reversed. Initially, areceived code-division-multiplexed signal is amplified, filtered andshifted to baseband frequence by a demodulator 51. The receivedcode-division-multiplexed signal is then despread by a plurality ofde-spreaders 52. The plurality of despreaders 52 may be embodied as aplurality of correlators or a plurality of matched filters. A pluralityof surface acoustic wave (SAW) devices alternatively may be used. Theoutputs of the plurality of de-spreaders are decoded and de-interleavedby a plurality of FEC decoders and de-interleavers 56, to produce aplurality of sub-channels of data. The plurality of sub-channels of datais multiplexed by a multiplexer 57 to generate a replica of the inputdata.

The modification to FIG. 2, shown in FIG. 4, includes having a data-ratecommand signal control the demultiplexer 31. Input data to thedemultiplexer 31, initially may pass through a buffer 29. The data-ratecommand signal controls the data rate of data from the demultiplexer 31.More particularly, the data-rate command signal determines the number ofdata channels having identical data and different data, in the pluralityof data channels from demultiplexer 31.

In the exemplary arrangement shown in FIG. 5, the command means,embodied as a command processor 59, and adder means embodied as amultiplicity of adders 53, is added to the embodiment shown in FIG. 3.The multiplicity of adders 53 is coupled between the plurality ofdespreaders 52 and the plurality of FEC decoders and de-interleavers 56,respectively. The command processor 59 is coupled to the plurality ofFEC decoders and de-interleavers 56, the multiplexer 57, and themultiplicity of adders 53. The command processor 59 has a communicationslink to the spread-spectrum traqnsmitter, for sending the data-ratecommand signal to the spread-spectrum transmitter.

The multiplicity of FEC decoders generates a syndrome signal from anerror rate of the multiplicity of added channels. In response to thesyndrome signal, the command processor 59 determines a desired-datarate, and generates a data-rate command signal having the desired datarate. The command processor 59 also generates the adder-control signal,used by the multiplicity of adders 53, for adding together a number ofdespread channels of the plurality of despread channels. The commandprocessor 59 generates a multiplexer signal having a number of decodedchannels to multiplex together. The multiplexer 57, in response to themultiplexer signal, sets the number of the multiplicity of decodedchannels to be multiplexed. The multiplexer 57 multiplexes themultiplicity of decoded channels and generates an estimate of the inputdata.

As illustratively shown in FIG. 4, the input data rate to thetransmitter is reduced by a data-rate command signal, which istransmitted from the spread-spectrum receiver. The data rate can bereduced by any factor of the width of the demultiplexer 31. For example,if 16 parallel chip-sequence signals were used, then the input data ratecan be reduced by a factor between 2 and 16. In a system, a buffer 29and flow control may be required. The demultiplexer 31 then outputsidentical bits to multiple lines that are fed to the encoders andinterleavers 32. For example, the data rate command may be to reduce thedata rate by a factor of 2. If 16 parallel chip-sequence signals wereused, two spreaders would be devoted to each bit; that is, thetransmitted power for each bit would be twice the power than in themaximum data rate situation.

In the exemplary arrangement shown in FIG. 5, the remote receiverfurther includes command processor 59. The error-rate and data ratecommand processor 59 reads or is fed the syndrome from the plurality ofFEC decoders and de-interleavers 56. In response to the syndrome, thecommand processor 59 determines a data rate. Thus, the data rate isdependent on the error rate of data being received and decoded by theplurality of FEC decoders. The command processor 59, based on the datarate determined by the command processor 59, generates the data-ratecommand signal, the adder-control signal, and the multiplexer-controlsignal. The command processor 59 generates the data-rate command signalshown in FIG. 4.

The receiver shown in FIG. 5 is configured, by way of example, for adata rate reduction by a factor of two. The outputs of every two matchedfilters are added together before the data sub-streams are decoded andde-interleaved. The add-control signal is generated by the commandprocessor 59. The multiplexer 57 then selects only half the decoderoutputs, i.e., half of the plurality of decoded channels, to combine toform the output data. By way example, the syndrome of the FEC decoder isused to measure the error rate. The error rate information is used togenerate the data rate command, which is transmitted to the base stationtransmitter. The error rate processor also controls the multiplexer 57and the adders 53 as it determines how many of the outputs from theplurality of despreaders 52 should be combined for the reduced errorrate.

FIG. 6 shows the despreaders 52 alternatively embodied as a plurality ofmatched filters 67. Equivalently, the plurality of despreaders may beembodied as a plurality of SAW devices, which mathematically areequivalent to a plurality of matched filters 67.

As illustratively shown in FIG. 7, the present invention also includes aspread-spectrum method for controlling the data rate at aspread-spectrum transmitter. The method includes the steps ofdemultiplexing 81, in response to a data-rate command signal, input datainto a plurality of data channels. The number of data channels in theplurality of data channels is determined from the data rate commandsignal.

The method includes FEC encoding and interleaving 82 the plurality ofdata channels as a plurality of FEC encoded and interleaved channels,respectively; and spread-spectrum processing 83 the plurality of FECencoded and interleaved channels as a plurality of spread-spectrumchannels. The plurality of spread-spectrum channels preferably areembodied with a plurality of orthogonal or quasi-orthogonalchip-sequence signals.

The method further includes the steps of combining 84 the plurality ofspread-spectrum channels as a code-division-multiplexed signal; andmodulating 85 and transmitting the code-division-multiplexed signal,which has the plurality of spread-spectrum channels, over acommunications channel.

At a spread-spectrum receiver, the method includes the steps ofdemodulating 85 or translating the code-division-multiplexed signal to aprocessing frequency; despreading 92 the code-division-multiplexedsignal into a plurality of despread channels, respectively; and adding93, based on an adder-control signal, at least two despread channels togenerate a multiplicity of added channels. The method includesgenerating 95 a syndrome signal from an error rate of the multiplicityof added channels; FEC decoding and de-interleaving 94 the multiplicityof added channels, and a multiplicity of decoded channels; and,determining 90, in response to the syndrome signal, a desired-data rate.The method further includes generating 90 a data-rate command signalhaving the desired data rate; generating, in response to the syndromesignal, the adder-control signal for adding together a number ofdespread channels of the plurality of despread channels; generating 90,in response to the syndrome signal, a multiplexer signal having a numberof decoded channels to multiplex together; and multiplexing 96 themultiplicity of decoded channels and an estimate of the input data. Thedata-rate command signal is sent over a communications channel to thespread-spectrum transmitter.

It will be apparent to those skilled in the art that variousmodifications can be made to the spread-spectrum communications,variable throughput reduction system and method of the instant inventionwithout departing from the scope or spirit of the invention, and it isintended that the present invention cover modifications and variationsof the spread-spectrum communications, variable throughput reductionsystem and method provided they come within the scope of the appendedclaims and their equivalents.

1. A communications system comprising: a transmitter, including, ademultiplexer for demultiplexing input data into a plurality of datachannels; a plurality of forward-error-correction encoders andinterleavers, coupled to said demultiplexer, for FEC encoding andinterleaving the plurality of data channels as a plurality of FECencoded and interleaved channels, respectively; a plurality ofprocessors, coupled to said plurality of FEC encoders and interleavers,for processing the plurality of FEC encoded and interleaved channels asa plurality of modulated channels; a combiner coupled to said pluralityof processors, for combining the plurality of modulated channels as amultiplexed signal; a receiver, including, a plurality of demodulatorsfor demodulating the multiplexed signal into a plurality of demodulatedchannels, respectively; a multiplicity of FEC decoder andde-interleavers, coupled to said plurality of demodulators for FECdecoding and de-interleaving the multiplicity of demodulated channels,as a multiplicity of decoded demodulated channels; and a multiplexer,coupled to said plurality of FEC decoders and de-interleavers, formultiplexing the multiplicity of decoded channels. 2-20. (canceled) 21.The communications system as set forth in claim 1, further including:said multiplicity of FEC decoders for generating a plurality of syndromesignals; and a command processor, responsive to the plurality ofsyndrome signals, for determining which channels in the plurality ofmodulated channels to delete from transmission over the communicationschannel.
 22. The communications system as set forth in claim 1, furtherincluding: said multiplicity of FEC decoders for generating a pluralityof syndrome signals; and a command processor, responsive to theplurality of syndrome signals, for employing erasure decoding forcorrecting errors.
 23. The communications system as set forth in claim1, said command processor, responsive to the plurality of syndromesignals, for sending a data-rate command signal to the transmitter. 24.A communications system comprising: a transmitter, including,demultiplexer means for demultiplexing input data into a plurality ofdata channels; encoder means for FEC encoding and interleaving theplurality of data channels as a plurality of FEC encoded and interleavedchannels, respectively; processor means for processing the plurality ofFEC encoded and interleaved channels as a plurality of modulatedchannels; combiner means for combining the plurality of modulatedchannels as a multiplexed signal; a receiver, including, demodulatormeans for demodulating the multiplexed signal into a plurality ofdemodulated channels, respectively; decoder means for FEC decoding andde-interleaving the multiplicity of demodulated channels, as amultiplicity of decoded channels; and multiplexer means for multiplexingthe multiplicity of decoded channels.
 25. The communications system asset forth in claim 24, further including: said decoder means forgenerating a plurality of syndrome signals; and command-processor means,responsive to the plurality of syndrome signals, for determining whichchannels in the plurality of modulated channels to delete fromtransmission over the communications channel.
 26. The communicationssystem as set forth in claim 24, further including: said decoder meansfor generating a plurality of syndrome signals; and command-processormeans, responsive to the plurality of syndrome signals, for employingerasure decoding for correcting errors.
 27. The communications system asset forth in claim 24, said command-processor means, responsive to theplurality of syndrome signals, for sending a data-rate command signal tothe transmitter.
 28. A communications method comprising the steps of:demultiplexing input data into a plurality of data channels; FECencoding and interleaving the plurality of data channels as a pluralityof FEC encoded and interleaved channels, respectively; processing theplurality of FEC encoded and interleaved channels as a plurality ofmodulated channels; combining the plurality of channels as a multiplexedsignal; transmitting the multiplexed signal having the plurality ofmodulated channels, over a communications channel; demodulating themultiplexed signal into a plurality of demodulated channels,respectively; FEC decoding and de-interleaving the plurality ofdemodulated channels, as a multiplicity of decoded channels; generatinga syndrome signal from an error rate of the multiplicity of decodedchannels; and multiplexing the multiplicity of decoded channels.
 29. Thecommunications method as set forth in claim 28, further including thesteps of: generating a plurality of syndrome signals; and determining,responsive to the plurality of syndrome signals, which channels in theplurality of modulated channels to delete from transmission over thecommunications channel.
 30. The communications method as set forth inclaim 28, further including the steps of: generating a plurality ofsyndrome signals; and employing, responsive to the plurality of syndromesignals, erasure decoding for correcting errors.